Wis. Admin. Code Department of Natural Resources NR 810.11
Community water systems with fire protection shall be operated so that under fire flow conditions the residual pressure in the distribution system is not less than 20 pounds per square inch at ground level. Water suppliers shall maintain current flow studies showing the fire flow capability of the system. Fire pumpers may not be connected to fire hydrants if 20 psi cannot be maintained in the system during operation of the pumpers. In addition, the public water system owner shall notify the fire chief in writing of the location of all fire hydrants that cannot be used by fire pumpers and color code or tag the affected hydrants. The department may require pressure and flow testing to determine whether adequate flows and pressures are available.
Wis. Admin. Code Department of Natural Resources NR 810.11